Computers use various cursor control mechanisms to provide a physical control over cursor placement on the computer screen. The most common form of cursor control device is a mouse. Because a mouse is used in a position physically remote from the computer, it is not the preferred cursor control device for portable or laptop computers. In these computers, users want the freedom to operate the computer without any additional external devices. One frequently used cursor control mechanism incorporated into portable computers is that of a pointing stick. These devices have been described in many patents including U.S. Pat. No. 5,966,117 to Seffernick incorporated herein by reference. The Seffernick device provides a pointing stick mechanism including the ability for sensing a z-axis deflection. This z-axis deflection can be used to provide the mouse click function in place of providing separate buttons on the chassis of the computer.
One problem with existing pointing stick devices is the height of the device above the keyboard of the computer. When the screen is folded over the keyboard to close the computer, heavy objects can be placed on top of the computer. The screen may deflect when loaded in this manner causing the center of the screen to be impacted by the pointing stick. As the load is increased, it is possible for the deflection to cause damage to either the pointing stick or the screen.
One approach to resolve some of the problems associated with pointing stick devices has been to mount the strain sensitive resistors on a supporting member rather than the shaft of the pointing stick. However, these devices have placed the shaft connection to the underlying substrate towards the center of the device with a supporting electrical connection towards the periphery of the device. This can result in poor performance because of the distance between the connection points. The ceramic material used for the substrate typically expands and contracts in response to temperature differently than the underlying printed circuit board to which the substrate is mounted. As the temperature within the computer increases or decreases, the connections between the substrate and the printed circuit board are therefore stressed. Placing the connections as close together as possible can minimize this harmful effect. An additional problem with traditional approaches is that as keys are pressed on the keyboard or as the computer is flexed slightly, the support for the pointing stick is correspondingly flexed. This can cause unwanted cursor movement. Placing the physical connections towards the center of the substrate similarly minimizes this effect.
The present invention overcomes this problem by providing a pointing device that is compact in design. The present invention is also easily manufactured and the structure is simplified over other compact pointing devices.
The present invention is directed to a pointing stick especially for use as a cursor control device for a computer that incorporates strain sensitive resistors. The pointing stick includes a shaft mounted to a substrate around the periphery of the substrate. The substrate is fixedly attached to a printed circuit board or other structure. The substrate carries at least one strain sensitive resistor. As the shaft is deflected, the substrate is stressed relative to its attachment to the printed circuit board which in turn causes the strain sensitive resistor to vary resistance to correspond to the desired cursor movement by the user.